Standard Endodontic Techniques
Kenneth Lyon United States
Standard root canal therapy is more clearly described as conventional endodontics. Most modern endodontic treatment involves removal of the irreversibly damaged pulp followed by cleaning and shaping of the root canal space and subsequent filling, or obturation, with a semisolid material and a sealer. Shaping of the canal is done by either hand or engine-driven instruments. Cleaning is done by irrigating the canal system with one of a number of solutions that may be antibacterial and have tissue-dissolving ability. Obturation is achieved with gutta-percha and a root canal sealer.
The cleaning and shaping phase of endodontic treatment is regarded as the most important. When the canal is clean, it is important that the system is not recontaminated by microorganisms. Because of the complex anatomy of the root canal system, complete disinfection is almost impossible to achieve. It is important, therefore, that any remaining microorganisms in the dentinal tubules are prevented from multiplying by the use of an antimicrobial dressing followed by three-dimensional filling. Recontamination from the oral cavity must be avoided, and the importance of a good coronal seal cannot be overestimated.
DIAGNOSIS OF ENDODONTIC DISEASE
Endodontic treatment is required when the pulpal contents are undergoing an irreversible degenerative inflammatory process or are necrotic and the tooth is needed as a functional part of the dentition. Many signs of the endodontically involved tooth may be observed at various times during the affected animal's distress. Localized facial edema or a fluctuant parulis or gumboil apical to the involved tooth would raise immediate suspicions of a dental abscess. Regional lymphadenopathy may be detected by palpation. Reduced biting pressure during play or aggression training may be noted, as may be reluctance to eat or refusal of food, especially hard or fibrous food, and the animal may even selectively eliminate harder items from its diet. To relieve discomfort during late signs of abscess development, the animal may constantly attempt to contact cool or cold surfaces and liquids. Fever may develop as the abscess reaches an acute stage. Radiographically, the periapical abscess or granuloma may appear as a circular radiolucent area at the apex of the affected tooth; bony trabeculation is reduced or absent. In the early stages of abscess formation, bony changes are not radiographically present. Because of this, peri-apical abscess cannot be eliminated from the differential diagnosis solely based on a negative radiographic finding.
Pulpectomy involves removal of the contents of the pulp chamber and canal. There are three major goals of veterinary endodontic therapy that should be sequentially attained for reasonable assurance of success.
1. Initially, the entire contents of the pulp chamber and canal should be removed with endodontic files and irrigation.
2. Using endodontic files, the canals should be cleansed and enlarged to give the canal a slight funnel shape.
3. The apex (or apices) of the treated tooth should be sealed and the canal packed with an endodontic filling material. Antibiotic therapy is recommended in conjunction with endodontic therapy
Dental radiographs are always an important part of endodontic therapy. The shape, length, width and direction of the root canal(s) are visualized on the radiograph. All endodontic procedures begin with radiographs. Access form of the canine teeth is made in the exact center of the mesial or facial surface of the crown just coronal to the gingival margin. Access form is always made on the occlusal surface of all posterior teeth. The mandibular first molar will have two roots. The initial point of penetration to establish a preliminary outline form is in the exact center of the mesial groove and the exact center of the distal cusp. There are three roots in the maxillary fourth premolar. The initial point of penetration to establish preliminary outline form is centered over the distal root canal slightly distal to the distal developmental groove. The palatal (mesio-lingual) root is penetrated at the palatal pit, nearly over the furcation between the palatal and mesio-buccal root. The initial point of penetration to the mesio-buccal root is centered on this cusp one-half the distance between the cusp tip and the gingival margin. A trans-coronal approach has also been described.
Debriding the Canal(s)
When access preparation has been completed and the pulp chamber is exposed, the contents of the chamber, if any, are removed using a barbed broach. A broach is a tapered steel wire, round in cross section, into which cuts have been made in the working end. These cuts create barbs, which flare from the shaft of the wire in an outward direction. These barbs entangle residual pulp content and remove it when the broach is withdrawn from the canal. The canal is then debrided and shaped using Hedstrom and/or K-type files.
A Hedstrom file is a tapered steel wire, round in cross section, whose flutes are cut in by a machine process. As the name implies, it is a file and thus the working action is on the withdrawal. The K-type file is a tapered steel wire, square or triangular in cross section, which has been grasped at the very tip of the wire and twisted. The action is to file or on withdrawal. This file can also be used in a reaming action by placing it in the canal to the first unforced contact, rotating a quarter turn clockwise and then withdrawing.
Root canal debridement can be aided with the use of a chelating agent such as EDTA (ethylene diamine tetraacetic acid). Its function is threefold: it helps debride the canal opening up dentin tubules, it softens the dentin making dentinal removal easier, and it lubricates the canal. As a dentin-softening agent, EDTA works very slowly. The EDTA is meant to chelate or remove metallic ions such as calcium by binding them chemically.
Throughout the debriding or filing process, the root canal must be recapitulated. A smaller diameter file is intermittently and finally inserted to the measured apical length and the small bits of debris that are packed into the apex are removed to insure total canal debridement. Recapitulation is a necessity for proper endodontic success. Irrigation The canal is irrigated with a solution of sodium hypochlorite (household bleach). It is able to lubricate, wash out debris, dissolve organic tissue and destroys almost all of the microorganisms found in the root canal system. The bleach should be irrigated from the canal with a final saline irrigation. When the canal(s) have been irrigated for the final time, residual moisture must be eliminated before the canal can be filled. This can be done by repeatedly inserting individual absorbent paper points into the canal. Successful endodontic therapy is best attained with a dry canal prior to the final filling procedure.
FILLING THE CANAL(S)
The goal of complete root canal treatment is the total three-dimensional obturation of the prepared root canal and pulp spaces. The foramina at the apex of the tooth are not the sole communication of the pulp spaces to the external surface of the root. Dentinal tubules on a microscopic scale, as well as accessory and lateral canals on a macroscopic scale, can and do communicate with the external surface of the root. It is therefore a requirement to seal the root canal throughout its preparation as at the apical foramina. This will prevent microorganisms from entering and reinfecting the tooth by percolation. Achieving an apical and coronal seal of the root canal is most important.
Obturation or the filling of the root canal is the culmination of the procedure in root canal therapy. The entire regimen of treatment to this point has been to establish the tooth in a biologic compatible status, and to shape and facilitate filling the canal. Failure to fully obturate and seal the canal will lead to endodontic failure. A combination of materials comes close to the ideal and affords an adequate root canal filling material: Gutta-percha and root canal sealer. Root Canal Sealers Gutta-percha alone is not capable of sealing a root canal. Even in the most precise adaptation to the prepared canal, microscopic spaces will exist and allow leakage. In order to achieve an adequate seal, root canal sealers are used in conjunction with gutta-percha to provide that measure of total obturation. Examples include Kerr Sealapex, Mynol Cement, AH-26, ESPE Ketac-Endo and Zinc Oxide with Eugenol.
Sealers are used to create and maintain an apical seal. The root canal cement or sealer is placed by utilizing lentulo spiral fillers on a reduction gear contra angle, with endodontic files, and/or by injection techniques. Gutta-Percha Gutta-percha is a purified, coagulated milky exudate of certain trees found in the Malayan Archipelago. It is closely related to rubber. When placing the gutta-percha, the master cone is selected and is inserted slowly into the canal to allow air and excess sealer to escape around the cone. The master cone size corresponds to the last file used when instrumenting the canal. Then a spreader is used by placing it into the canal between the master cone and the canal wall. Lateral condensation is used to place pressure in an apical direction. The taper of the spreader is the mechanical force that laterally compresses and spreads the gutta-percha. The spreader is creating the space for an additional accessory cone. Gently withdraw the spreader form the root canal using a back and forth rotating movement and immediately insert a prepared accessory cone into the newly shaped space. Immediate placement is necessary since gutta-percha will rebound after the spreader is removed. The accessory cone should be slightly smaller than the spreader. Repeat this procedure of laterally condensing the gutta-percha and adding accessory cones until the canal has been fully filled to the cervical line. A heat transfer instrument is used to vertically condense the cervical portion of the canal and sear off the excess gutta-percha at a level 2 mm apical to the cervical line. A Glick No.1 or a Touch 'n' Heat (EIE/Analytic Technology, Orange, CA) may be used. Make a radiograph to demonstrate the completeness or incompleteness of the root canal filling. If the canal is not completely obturated, the gutta-percha will need to be removed and the procedure started over again. Once obturation is confirmed, the coronal chamber must be thoroughly cleaned. All sealer and gutta-percha fragments must be removed. Clean access sealer using alcohol soaked cotton pellets.
Following filling of the canal a restoration can be placed, using either composite or amalgam, to seal the access opening and fracture line. First, the root canal filling materials are covered with a layer of glass ionomer or other intermediate restorative material. Next, an under cut cavity preparation is completed. If composite is being used, the enamel is etched, rinsed, and a bonding agent applied and cured. Finally, the composite or amalgam is placed, finished, and polished.
EVALUATION OF OBTURATION
Radiographic evaluation is the only immediate method of assessment of the obturation. Study the obturation radiograph for radiolucencies indicating voids or incomplete obturation. The filling material should be of uniform density from apical to coronal aspects with sharp and distinct margins. The material should extend to the working length and should reflect the shape of the canal, tapering from coronal to apical. Further evaluations should be scheduled at two weeks and six weeks, followed by radiographs at six months and then yearly thereafter.
WSAVA Contact Information